Dark background image isn't correctly set up on iOS

[CoocooFroggy]

Describe the bug

The dark splash screen background_image_dark isn't correctly configured with LaunchBackground.imageset, and only the light background_image is used.

Configuration

flutter_native_splash:
  background_image: "assets/background_light.png"
  background_image_dark: "assets/background_dark.png"

Device (please complete the following information):

• Device: Simulator, iPhone 14 Pro (but likely happens on every device)
• OS: iOS 16.1 (but likely happens on every version)

To Reproduce
Steps to reproduce the behavior, using the example app:

1. Create a new flutter app
2. Add flutter_native_splash: ^2.2.14 to dependencies
3. Add the above flutter_native_splash configuration to pubspec.yaml
4. Add images to the project under assets/background_light.png and assets/background_dark.png
5. Run flutter pub run flutter_native_splash:create

Screenshots

Additional context
LaunchBackground's Contents.json

{
  "images" : [
    {
      "filename" : "background.png",
      "idiom" : "universal",
      "scale" : "1x"
    },
    {
      "idiom" : "universal",
      "scale" : "2x"
    },
    {
      "idiom" : "universal",
      "scale" : "3x"
    }
  ],
  "info" : {
    "author" : "xcode",
    "version" : 1
  }
}

Issue is the same as #439.

[jonbhanson]

I will push out an update soon that should fix this.